Patent application title: Sizing Cage Adjustment

Abstract:

The present invention describes a blown film extrusion line (1), which has
the following features: an annular die gap, from which the film tube
(9) can be extruded, a flatness unit (7,13) or nip rolls (8), which fold
the film tube (9), a calibration basket (20,30), which is disposed
between the die gap and the flatness unit (7,13) or nip rolls (8) and
which comprises at least two film-guide elements (31), using which the
film tube (9) can be guided in such a way that it retains its round
cross-section, the diameter of the film tube (9,43) being adjustable by
changing the relative position of the at least two film-guide elements
(31).
The coupling means (32,33,35,38,39), which couple the movement of at least
two film-guide elements (31) to each other, are particularly
advantageous.

Claims:

1. Blown film extrusion line (1), which has the following features:an
annular die gap, from which the film tube (9) can be extruded,a flatness
unit (7,13) or nip rolls (8), which fold the film tube (9),a calibration
basket (20, 30), which is disposed between the die gap and the flatness
unit (7,13) or nip rolls (8) and which comprises at least two film-guide
elements (31), using which the film tube (9) can be guided in such a way
that it retains its round cross-section,the diameter of the film tube
(9,43) being adjustable by changing the relative position of the at least
two film-guide elements (31),said blown film extrusion line being
characterized by coupling means (32,33,35,38,39), which couple the
movement of at least two film-guide elements (31) to each other.

2. Blown film extrusion line (1) according to claim 1characterized in
thatthe coupling means (32,33,35,38,39) are designed in such a manner
that the at least two film-guide elements (7) can be moved, in the case
of active coupling means, in the radial direction (r) of the film tube
(9) only by the same amount of distance.

3. Blown film extrusion line (1) according to claim 1characterized in
thatthe coupling means comprise actuators, which can be controlled by a
common control device.

4. Blown film extrusion line (1) according to claim 1characterized in
thatthe actuators are linear drives or that the actuators can be used to
generate a torque, which can be transferred to the functional pairs
composed of spindles and nuts in such a manner that the torque is
converted into a force.

5. Blown film extrusion line (1) according to the preceding
claimcharacterized in that the actuators can be used to generate a
torque, which can be transferred to the functional pairs composed of
spindles and nuts in such a manner that the torque is converted into a
force and that the rotational movement of the different actuators can be
regulated.

6. Blown film extrusion line (1) according to claim 1characterized in
thatthe coupling means (32,33,35,38,39) comprise elements for the
mechanical forced coupling of the movement of at least two film-guide
elements (31).

7. Blown film extrusion line (1) according to the preceding
claimcharacterized in that theelements for the mechanical forced coupling
comprise a sliding bearing (33).

8. Blown film extrusion line (1) according to claim 1characterized in
thatthe elements for the mechanical forced coupling comprise at least one
rod (32), which is mounted in at least one sliding bearing (33).

9. Blown film extrusion line (1) according to the preceding
claimcharacterized in thatat least one rod (32) is mounted in the at
least one sliding bearing (33) in such a manner that the rod (32) is held
tangentially to the peripheral surface of the film tube (9,43).

10. Blown film extrusion line (1) according to the preceding
claimcharacterized in thatanother sliding bearing (33) is provided, which
guides the at least one rod (32) or an element that is mechanically
connected to the rod (32).

11. Blown film extrusion line (1) according to claim 1characterized in
thatthe at least one rod (32) is mechanically articulated either directly
or via an intermediate element pivotally on at least one holding rod
(35).

12. Blown film extrusion line (1) according to the preceding
claimcharacterized in that the at least one holding rod (35), for its
part, is pivotally articulated on a frame (44) of the calibration basket.

Description:

[0001]The invention relates to a blown film extrusion system in accordance
with the preamble to Claim 1.

[0002]Such blown film extrusion lines are known from the prior art and are
already in use since long. Such lines are supplied with plastic in
granulated form, which is then plasticized in extruders under the effect
of high pressure to form a viscous mass. This mass, which is of high
temperature due to the pressure, is provided with an annular shape in a
blown film die and is discharged from the blown film die through a
tubular die. The mass forms a film tube immediately after leaving the
tubular die. However, the diameter of this film tube can be changed since
the latter has not yet cooled down completely. Usually, the diameter is
increased by blowing compressed air into the interior of the film tube.
In order for the film tube to have a constant diameter at all times, it
is guided at a distance from or directly along film-guide elements. This
arrangement of the film-guide elements is referred to as "calibration
basket" in the field of blown film extrusion lines. After passing through
the calibration basket, the film tube that is now solidified is guided
along additional film-guide elements, which flatten the tube. This
flatness unit supplies the film tube to a squeezing device so that the
film tube forms a two-ply film web. The term "squeezing" is also meant to
connote both the complete and incomplete flattening of the film tube.
Processing steps such as cutting the film longitudinally along the folded
edges can further follow the incomplete flattening process of the film
tube.

[0003]The film-guide elements of the calibration basket can be
two-dimensional elements made of a slippery material, but they can also
be rollers. Teflon rollers, felt rollers, pearl strips, and brush-like or
broom-like elements can be used as film-guide elements. The objective of
all these measures is to guide the film reliably and to apply a force on
the film to the fullest extent while also preventing any damages to the
still hot, freshly extruded film. For quite some time, calibration
baskets are therefore being used, which comprise film-guide elements,
which comprise an air cushion on the side that faces the tube and which
guide the tube in a contact-free manner.

[0004]For this purpose, these tube guide elements are penetrated by bores,
to which compressed air is applied on that side of the film-guide
elements that is turned away from the film tube. The compressed air
flowing through the bores, which have a diameter of 0.5 mm by way of
example, keeps the film tube at a distance so that the latter is guided
in a contact-free manner. This helps prevent damages to the film tube.

[0005]However, the bores must be provided at a certain distance from each
other so that the film-guide elements do not lose their stability. But
this results in the air cushion, which guides the film tube, not acting
uniformly on the periphery of the film tube. This adversely affects the
accuracy of guidance. The result is greater inaccuracies in the diameter
of the film tube. The film tube also tends to flutter due to the
non-uniform application of compressed air.

[0006]It is therefore suggested in EP 1 488 910 A1 to use a porous or
micro-porous material for designing the film-guide elements, which porous
or micro-porous material extrudes air through a plurality of small holes
and thus produces a particularly suitable air cushion. A porous,
preferably a micro-porous material--for example, sintered material, is
suggested to be used as the material, which contains this plurality of
small holes.

[0007]Such materials comprise a plurality of continuous pores. It is
therefore possible to apply compressed air to that side of the film-guide
elements that is turned away from the film tube. This compressed air then
forms an almost uniform air cushion on that side of the film-guide
elements that faces the film tube. This air cushion can be used to guide
the film tube with high quality.

[0008]Preferably sintered material is used as the material that has these
properties.

[0009]The aforementioned types of film-guide elements usually guide a
portion of the periphery of the tube. That surface of the film-guide
elements that faces the tube and is used to guide the film or that
surface of the film-guide elements that supports the air cushion guiding
the tube is curved in order to mate perfectly with the round peripheral
surface of the circle. This can be seen clearly, for example, in EP 1 488
910 A1 mentioned above.

[0010]If the format--thus in this case, the diameter of the
cross-sectional surface--of the film tube is to be changed in such a
device, it is necessary to change the relative positions of the
film-guide elements. This is usually achieved by changing the position of
the film-guide elements in the radial direction of the film bubble. For
this purpose, the film-guide elements in EP 1 488 910 A1 are provided
with individual adjusting means. These adjusting means must be operated
carefully in order to ensure that the round shape of the film
cross-section is retained.

[0011]It is the object of the present invention to facilitate these
adjusting operations.

[0012]This object is achieved by coupling means, which couple the movement
of at least two film-guide elements to each other. Another advantage of
using these coupling means is the speed gain in the adjusting operations
since the coupling can enable the adjusting processes to be performed
simultaneously. It even appears possible to change the diameter of the
film tube during the operation of the blown film extrusion line. This was
not possible so far due to restrictions imposed by the individual
adjustability of the position of the guide elements. It shall be
understood that the term "at least two guide elements" refers to any
number between two and the total number of film-guide elements. Different
exemplary embodiments of the invention can be implemented automatically
by a control unit and can thus be combined with a strongly automated
order change on a blown film extrusion line.

[0013]Coupling means, which couple the movement of guide elements in such
a way that the respective guide elements move in the radial direction of
the film bubble by the same amount of distance, are advantageous. The
coupling process naturally requires the "start-up" of the coupling means.
Thus, it is naturally necessary for exclusively mechanically operating
coupling means to be actively linked to the coupling guide elements.
However, such an active connection can usually be separated by detaching
or loosening reversible connecting elements--such as screws. Also in the
case of a common open-loop or closed-loop control of drives, which act on
different guide elements, the coupling--also often referred to as
"virtual axis"--can be designed such that it can be activated or
deactivated. An automatic, largely manual adjustment, in accordance with
the invention, of the position of the guide elements can contain linear
drives or motors. If torque-providing motors are used, it is advantageous
to convert their torque using spindles and nuts into force. This force
can be used to move the film-guide elements on a slide guide by way of
example.

[0014]Additional preferred embodiments of the invention are defined in the
sub claims and illustrated in the drawings. In the individual figures:

[0015]FIG. 1 shows a blown film extrusion line according to the prior art

[0016]FIG. 2 is a plan view of a calibration basket of the invention; the
angle of view is indicated by arrows as in FIG. 1

[0017]FIG. 3 is a plan view of the same calibration basket of the
invention, where a smaller film-tube diameter is used than the one in
FIG. 2; the angle of view is indicated by arrows as in FIG. 1

[0018]FIG. 4 is a plan view of a calibration basket of the invention,
where a smaller film-tube diameter is used than the one in FIG. 2; the
angle of view is indicated by arrows as in FIG. 1

[0019]FIG. 1 shows a blown film extrusion line 1 known from the prior art.
Plastic is supplied to the filler neck 4 and is then plasticized in the
extruder 3. The resulting mass is supplied via a connecting line 14 to
the blown film die 5 and forms a film tube 9. The film tube 9 leaves the
blown film die 5 through a tubular die (not visible in the Figure) in the
transport direction z. Due to the supply of compressed air by the blower
outlet 12 [sic: 15], the film tube is expanded immediately after leaving
the blown film die 5. But, the diameter of the film tube 9 is delimited
by the calibration basket 20. Inside the calibration basket 20, the film
tube 9 is guided by plates 28, through which compressed air is directed
toward the film tube. The calibration basket 20 further consists of a
frame 21 and cross beams 22 and 6. After leaving the calibration basket
20, the film tube 9 arrives into a flatness unit 21, in which the film
tube is transformed almost or completely into a two-ply film web. The
film tube 9 is guided between pairs of guide elements 7, 13, which assume
positions located at an increasingly small distance from each other in
the course of the transport direction z. The film is completely flattened
by means of a squeezing device consisting of a pair of nip rolls 8. The
film web 9 can now be guided by a reversing device (not shown), or the
film web 9 can be supplied, as in the case of the device illustrated,
directly via deflecting rollers 10 to a wind-up unit 11, where the film
web 9 is processed to form a reel 12.

[0020]FIGS. 2 to 4 show a plan view of a calibration basket 40 [sic: 30],
which guides a film tube 43 by means of the film-guide elements 31. The
arrows d2 to d4 clearly show that the diameter of the film bubble 43
reduces increasingly in the FIGS. 2 to 4. The diameter of the film bubble
is defined inter alia by the manner in which the film-guide elements 31
are positioned on the film tube 43. This positioning range of the
film-guide elements is coupled to the calibration basket of the invention
in such a manner that those surfaces of the film-guide elements that face
the tube 43 always abut tangentially against the round cross-sectional
area of the tube 43. This state can also be described in that the normals
on these surfaces, as shown in all three FIGS. 2 to 4, constantly point
at the center of the tube 43, which, for its part, is located over the
center of the blown film die 5 in the case of an optimum alignment. This
state can be brought about advantageously by an articulation 36 of the
film-guide elements about an axis, which is located parallel to the
principle axis of inertia of the film tube 9. This articulation 36 should
be provided at a holding element like the holding rod 35. As a result,
the film-guide element 31 can swivel freely--at least in an acute angle
range--or be guided by another element of the calibration basket--here
the coupling rod 32.

[0021]In the present exemplary embodiment, the surfaces 42 are provided
with an arcuate design, when seen from the observer's angle of view (in
the r-φ-plane), in such a way that the surfaces 42 mate exactly with
the round cross-sectional shape of the tube 43. The surfaces 42 here
consist of perforated or porous, preferably sintered material. The
application of compressed air to the inner sides of the surfaces 42
results in an air cushion on that outer side of the surface 42 that is
facing the tube. With the help of this air cushion, the guide element 31
guides the film in a contact-free manner. However, a film-guide element
could also guide the tube by using a brush, a roller or a sliding
surface.

[0022]The positive effect of the ability to change the radius of curvature
of that surface 42 of the film-guide elements 31 that is facing the tube
43 is evident. This ability to change the radius of curvature of surface
42 can be brought about, for example, by additional actuators, which
curve this surface. It can thus be ensured that the surface 42 facing the
tube rests against a large surface of the tube 43 when the radius of
curvature of the tube changes as a result of a format adjustment.

[0023]In the present exemplary embodiment, the film-guide elements 31 are
connected in a rotationally fixed manner to the coupling rods 32. The
coupling rods are guided using sliding bearings 33 in such a manner that
the coupling rods are always oriented tangentially to the film bubble 43.
This is achieved here by guiding each coupling rod by means of two
sliding bearings 33. The two sliding bearings assigned to the different
rods are illustrated one on top of the other in the Figures. The
film-guide elements 31 are also linked rotatably via the articulation 36
on the holding rods 35. The film-guide elements 31, for their part, are
again linked rotatably via the articulation 37 to the rotatable levers
38, which are attached preferably rotatably to the base frame 44. The
levers 38 are connected to each other by means of their articulations 40
and 41, located at both ends, and the coupling rods 39 of the levers.

[0024]In the case of a calibration basket, it is advantageous to combine
together the several planes of functional elements shown in the Figures.
Thus, several film-guide elements 31 will usually be disposed one after
another in the axial direction of the film tube z. The positions of the
film-guide elements 31 disposed one after another in the axial direction
can be staggered with respect to one another in the circumferential
direction φ of the film tube.